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Axial flow fans and ducts

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... CVD by the second half of the last century has shown to be attractive for the performance increase of axial-flow rotors [4] especially when blades were originally designed according to the free vortex criterion [5]. In fact, CVD allows to overcome total pressure limitations of low hub-to-tip ratio FVD rotors which unavoidably feature low loaded bladings to avoid the aerodynamic stall of the spanwise blade region close to the rotor hub [6]. ...
... Then, a blade design which assures constant ε s along the whole blade span is required. The selected cascade should achieve the highest lift-to-drag ratio during operation with the mean-radius velocity triangles obtained in previous step I. 1 (some well-established criteria to perform this task are recalled in [6]). Then, the airfoil section of the cascade selected for the blade mean-radius is employed along the whole blade span, so that the resulting blade features span-wise constant chord (l), camber (θ ) and thickness (s). ...
... The fan selected for the implementation of the presented procedure aimed at increasing the efficiency is a 1:2 scale model of an industrial rotor-only tube axial fan featuring external diameter equal to 630mm and total pressure coefficient equal to 0.0202, flow-rate coefficient equal to 0.088 and a quite high peak total efficiency (about 0.64). A reverse engineering analysis process suggested that the blades are likely to be constituted by envelopes of thick cambered plates sections with rounded leading and trailing edges and progressive trailing edge thinning, like those described in [6]. Tab. 2 reports the other main features of the scaled model fan and the photograph of its rotor blade (see, "Model" column). ...
... The focus of research on fan aerodynamic design is therefore moving away from the classic basic design methods that were widely adopted before the development of reliable CFD tools for the design process. A comprehensive review of axial-fan design up to the 1970 is given in Ref. [4], whereas an informative account of state of the art of axial-fan design before the end of the last millennium can be found in Ref. [5]. ...
... These charts were obtained from the application of a mean-line model conceived to estimate the aeraulic efficiency of tube-axial fans having blade load in agreement with the constant swirl distribution at the rotor exit. The mean-line model is based on a theoretical analysis of fan performance and energy losses in annular cascades, inspired by that suggested by Wallis [5] for free vortex design fans. The previous work of the current authors [15] also reports the detailed description of the model and its experimental validation. ...
... The design of the USW28 blading is the result of a two-step method that works without any CFD support. The first step (step I, in the following) leads to an intermediate blade by means of a reduced version of the "quasi-2D" design method for nonfree-vortex blades originally conceived by Kahane [23], then adapted to axial fans by Wallis [5] and, finally, formalized in Ref. [16] with the name "Kahane-Wallis method." The second step (step II, in the following) generates the improved blade using a simplified version of the "quasi-3D" step, named "Q3D" in the forward-swept blades design method suggested by Vad [6]. ...
Conference Paper
This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors ago with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high efficiency industrial fans. To this end, the method has been applied to a 315mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed a fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560mm industrial fan.
... k multiplane interference factor, C L C L i , (cf. [1]), [-]. T rotor torque due to aerodynamic contributions, [Nm]. ...
... Both cascade and isolated airfoil selection techniques are considered valid within their own respective ranges: high solidity rotors (σ 1 all along the span) for the first case and low solidity (σ 0.7) for the second. In case of medium pressure-rise machines, which feature high solidity close to the root and low solidity next to the tip, the modified isolated airfoil approach is commonly employed (e.g., the one developed by Wallis [1]). The use of this method for fans application is quite consolidated. ...
... Both the approaches enabled to achieve successful designs in their respective application field. For axial compressors the isolated airfoil technique was soon abandoned anyway [4], while both the approaches remain valid for axial fan blade design, depending on rotor solidity [1,4]. The cascade approach was experimentally verified with tests on actual low-speed compressor rotors, showing good agreement with wind tunnel data in terms of design turning angle [9,10] and pressure distribution [11]. ...
Conference Paper
Both cascade and isolated airfoil methods are considered valid in axial fan blade design, for high (σ≳1) and low (σ≲0.7) solidities respectively. For bladings that feature intermediate solidities the modified isolated approach is commonly employed. This method uses isolated airfoil data, with proper adjustments to take into account multiplane interference effects. Contrarily, the literature does not refer about modifications of the cascade approach to design medium solidity fans. Such method would use cascade data, properly adjusted for the blade sections at lower solidities. Thus, with the aim of comparing these two opposite design approaches (modified cascade versus modified isolated) for medium solidity blades, two free-vortex blading were designed for a 315 mm rotor-only axial fan and experimentally tested. CFD analyses were performed as well to obtain the local flow features. NACA-65 series airfoils were employed, as both cascade and isolated data are available for chord Reynolds numbers typical of axial fans applications. Results highlight the differences between the two approaches. Finally, a mixed approach that employs both isolated and cascade data is suggested as the most accurate one. Moreover, results also show the detrimental effects of the low chord Reynolds numbers on the performance of the blades. This effect should be taken into account in blade design for small-to-medium size machines. Copyright © 2016 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
... The tube-axial configuration (i.e. rotoronly fans, see Fig. 1b) is by far the most used in industrial applications of single stage low-speed axial fans [1]. Vane-axial units (i.e. ...
... Rotor-only fans usually feature hub-to-tip ratios in the range 0.25<ν <0.5. Rotor blades are usually of arbitrary vortex design type [1], to allow higher pressure rise when external dimensions and/or rotational speeds are constrained. The success of this fan type is due to its intrinsic simplicity, which corresponds to the cheapness of purchase, installation, and maintenance. ...
... The success of this fan type is due to its intrinsic simplicity, which corresponds to the cheapness of purchase, installation, and maintenance. In addition, the absence of fixed bladings is beneficial for noise emissions because it avoids acoustic interaction between rotating and steady Wallis [1] suggests that rotor-only machines should be employed for low pressure rise applications, when the ratio between the mean axial velocity c a and the blade tip speed U, (i.e. the flow factor φ), is less than 0.2. Qualitatively, this means that the low total pressure requirement can be achieved with a limited airflow swirl at rotor exit that does not justify the use of the straightener. ...
Conference Paper
Tube-axial fans are widely used in industrial applications because of their compactness, simplicity, and low cost. However, the achievable fan pressure rise is generally penalised by the absence of a straightener and diffuser, and the consequent waste of tangential and axial dynamic pressures at the fan outlet. The corresponding fan efficiency drop might not comply with stringent regulations like the European Directive for energy-related products. Thus, operation ranges of high efficiency need to be clearly defined in the preliminary design phase, especially when constraints on maximum size and/or rotational speed are imposed. This paper proposes analytical formulas and charts to evaluate the efficiency of the tube-axial fan configuration (with or without tail-cone diffuser) when constraints on fan size and/or speed are additional design requirements. The analytical formulas and charts have been validated against experimental data. On this basis, a preliminary design criterion is suggested for high-efficiency tube-axial fans featuring arbitrary vortex design blades of constant swirl type. The criterion is used to design a 315 mm low-to-medium pressure tube-axial fan that is able to operate at a constant aeraulic efficiency peak of approximately 0.6 for blade positioning angles in the range 20° to 30°. Copyright © 2016 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
... Kahane states that "[..] spanwise load distributions differing from the free-vortex type may be desirable for designs in which a high-pressure-rise-rotor is required". On the contrary, Wallis (1983) indicates arbitrary-vortex design to be suitable for low hub-to-tip ratio rotor-only fans with relatively demanding pressure-rise requirements (e.g., for cooling-tower applications), in particular to reduce the aerodynamic loading close to the hub to avoid blade overlapping. Wallis (p. ...
... The performance of the fans in Tab. 1 has been organized in the graphs of Figure 2. It must be noticed that free-vortex fans are not numerous in the rotor-only configuration, while arbitrary-vortex rotors are by far the largest group (e.g., Wallis (1983)). From the Φ − Ψ F T P graph in Fig. 2a) it appears that forced-vortex fans operate at higher pressure and flow coefficients than the classical Cordier line (Lewis, (1996)), while most of the arbitrary-vortex fans show the opposite behavior (lower flow-rates and pressure rises). ...
... Among the three classes, free-vortex best fits the Cordier-line while forced-vortex fans operate at lower σ−δ conditions, confirming what already observed by Bamberger (2015). However, most of high-efficiency arbitrary-vortex fans lie above the Cordier line (i.e., at higher flow-rates and lower pressure rises for a given diameter and rotational speed), thus confirming the qualitative indications reported by Wallis (1983). It must be noticed that, regardless of the vortex-criteria, η F T P at BEP/DP are slightly affected by the value of the corresponding flow-coefficient (Masi et al., 2016): most efficient fans (η F T P between 60% and 77%) feature flow-coefficients Φ ranging between 0.12 and 0.31 (see Tab. 1). ...
Conference Paper
Full-text available
Rotor-only axial fans feature rotors designed according to different vortex criteria. Nowadays the literature does not exhaustively clarify when a specific swirl distribution has to be used and which are the advantages/drawbacks in terms of fan performance and efficiency. A review of the experimental performance of rotor-only axial fans designed with different vortex criteria is summarized here in Φ − Ψ and σ − δ (specific speed - specific diameter) graphs to identify the best operating conditions of each design. Four rotor-only axial fans(two free-vortex, a constant-swirl and a rigid-body swirl one) are tested on an ISO-5801-A rig. For two of them, flow velocities at rotor exit are measured with a 5-hole probe. The result is an experimentally based map around the Cordier curve for rotor-only axial fans. Indications on the best Φ − Ψ range for fans designed using different vortex criteria are provided and explained. The effects of increasing the tip clearance on the rotor performance at design duty are investigated as well.
... Blading design for axial fans is quite a mature science, based on the principle of Aerodynamics. The classic design methods presented in the literature are basically sequences of operations (e.g., [1,2]). Once carried out, these operations finally provide a blade geometry that is expected to induce the required velocity triangles in the airflow, eventually with the highest efficiency achievable. ...
... The basic differences analyzed within this work (i.e., the choice of the airfoil, the choice of the solidity distribution, the stagger angle computation and the selection of the number of blades) are some of the most relevant. Regarding a basic design aspect as the bladeelement stagger angle ξ for example, some authors (e.g., [3][4][5]) compute this value with respect to the inlet velocity W 1 , while others (e.g., [1,6,7]) with respect to the mean W m one. The disagreements between the various methods are scarcely treated in the technical literature and generate confusion in the mind of the unexperienced fan designer, who starts facing with the duty of the aerodynamic blade design. ...
... The isolated airfoil approach (with proper modifications to account for the multiplane interference effects) was shown to be accurate even in case of medium solidity rotors [16]. The fan designer must have a clear picture of the airfoils that can be used for axial fan applications: an analysis on some of these sections is reported by Wallis in [1,17], while in Tab. 2 a summary of the airfoils suggested and/or used by some authors is presented. ...
Conference Paper
Some methodological differences exist among the design methods for axial-flow fans. These differences generate confusion in the mind of the unexperienced fan designer, who is unaware of which method ensures the achievement of the requiredpressure rise at highest efficiency. In this work three important differences that appear comparing the classic methods of fan blading design are highlighted and analyzed: i) the choice of the airfoil, ii) the choice of the solidity distribution, and iii) the computation of the stagger angle of the blade elements. A fourth aspect regards the selection of the rotor number of blades. This aspect is treated in relation to the dubious applicability of the drag annulus correlation by Howell to low hub-to-tip ratio fan design and analysis. CFD simulations are performed on three case-study rotor-only fans, comparing blades systematically designed varying the airfoils (British C4 vs American NACA-65), the solidity distribution (Diffusion Factor criterion against the arbitrary selection of the blade-element lift coefficient) and the computation of the stagger angle (with respect to the inlet flow velocity or the mean one). The accuracy of XFOIL-predicted data at low Reynolds number (e.g., 300000) in designing smallto-medium fans is discussed as well. For each of the previous design aspects, results suggest the best indication among those suggested in the classic literature to achieve fan requirements.
... A design study of an air-cooled heat exchanger fan at Stellenbosch University was undertaken by Bruneau in 1994 [2] resulting in the B2 fan. The design methodology used by Bruneau was largely based on the work of Wallis [3] and Dixon [4]. The B2 design has been shown to give improved performance at off design conditions as well as operating at a high total-to-static efficiency [5]. ...
... The technique assumes free vortex flow distribution through the fan and sufficiently low solidity at every point in the blading so that isolated aerofoil theory can be used. According to Wallis [3] isolated aerofoil data can be used when specific solidity and stagger conditions are met. As these parameters are unknown at this stage we assume that this is the case. ...
... Equation 2 is derived from the definition of total-to-static pressure, by subtracting the dynamic pressure component. Hub swirl ratios are limited to the values proposed by Wallis [3]. ...
Conference Paper
An axial flow fan design methodology is developed to design large diameter, low pressure rise, rotor-only fans for large air-cooled heat exchangers. The procedure aims to design highly efficient axial flow fans that perform well when subjected to off design conditions commonly encountered in air-cooled heat exchangers. The procedure makes use of several optimisation steps in order to achieve this. These steps include optimising the hubtip ratio, vortex distribution, blading and aerofoil camber distributions in order to attain maximum total-to-static efficiency at the design point. In order to validate the design procedure a 24 ft, 8 bladed axial flow fan is designed to the specifications required for an aircooled heat exchanger for a concentrated solar power (CSP) plant. The designed fan is numerically evaluated using both a modified version of the actuator disk model and a three dimensional periodic fan blade model. The results of these CFD simulations are used to evaluate the design procedure by comparing the fan performance characteristic data to the design specification and values calculated by the design code. The flow field directly down stream of the fan is also analysed in order to evaluate how closely the numerically predicted flow field matches the designed flow field, as well as determine whether the assumptions made in the design procedure are reasonable. The fan is found to meet the required pressure rise, however the fan total-to-static efficiency is found to be lower than estimated during the design process. The actuator disk model is found to under estimate the power consumption of the fan, however the actuator disk model does provide a reasonable estimate of the exit flow conditions as well as the total-to-static pressure characteristic of the fan.
... Tip clearance is an important factor in blade tip configuration with various studies showing a correlation between tip clearance and fan performance 3,7 . Wallis states that, "Provided the tip clearance does not exceed 1% of the blade height no adjustments to design pressure duty or fan efficiency are necessary." ...
... The flow mechanisms in the tip region are complex with interactions between flow over the casing wall and the fan tip leakage flow. A secondary vortex exists on the convex surface at the blade tip due to flow turning 7 . This flow has a radial direction leaking over the blade tip through the gap between the blade and the duct wall. ...
... The optimum tip clearance given by these tests was 2 mm, which resulted in a peak fan static efficiency of 60.3% as well as giving the best static pressure rise. This result is in line with the findings of Wallis and Kroger and Venter 3,7 . Lyon (France), 15 -17 April 2015 ...
Conference Paper
Full-text available
Large diameter axial flow fans used in air-cooled condensers (ACC) are major power consumers in in ACC units, therefore it is desirable to make them as efficient as possible. It is well known that the blade tip region has a substantial influence on the performance of such fans. Several tests were performed on a B2 axial flow fan in order to determine the effect of tip configuration on the performance of the fan. These included the testing of blade tip modifications as well as tip clearance. The results show that tip clearance is a major contributor to fan performance and that blade tip modifications can improve fan performance at larger tip clearances. An empirical model for tip clearance is also presented.
... . The primary function of this well-known diagram is identifying the operational range that pertains to each type of machine (i.e., axial or centrifugal) [28]; nonetheless, several authors used and still use it in the preliminary design phase to select the fan diameter D or the rotational speed n, even if this practice is not encouraged by others (e.g., [29,30]). Regardless of its use, the Cordier diagram represents a milestone in the history of turbomachine design and is still a reference for any low-speed fan and pump designer. ...
... In the same reference, the authors addressed the design of rotor-only fans with low hub-to-tip ratios (ν = 0.38) and arbitrary vortex blades (i.e., NFV designs), presenting the experimental validation of a simple analytical design method. This approach includes a simple algorithm for the computation of the meridional flow distribution, that had been originally presented by Wallis in the third edition of his book [30]. It is remarkable that Wallis' method is actually the development of the equations presented by Ruden [18] and Kahane [26] around 50 years before. ...
... The publications considered were of three types: (i) technical books on the subject; (ii) papers on peer-reviewed journals and conference proceedings; and (iii) technical reports from military and civil agencies. Several sources were identified in the bibliography of books (Wallis [30] and Eck [1], in particular) and of the papers. Researches on modern on-line electronic databases were conducted as well. ...
Article
Full-text available
The paper presents a historical overview of the developments of aerodynamic design methods for low-speed axial-flow fans. This historical overview starts from the first fan applications, dating back to the 16th century, and arrives to the modern times of computer-based design techniques, passing through the pioneering times of aerodynamic theories and the times of designing before computers. The overview shows that the major achievements in the axial fan design discipline have actually been related to other technological fields, such as marine and aeronautical propulsion, as well as to the development of wind tunnels. At the end of the paper, the reader will have acquired a complete panorama of how the historical developments of the discipline have brought us to the current state of the art.
... In order to achieve the same fan performance for both directions of flow, blades are designed with straight symmetrical profiles in the shape of the ellipse [1][2][3]. Due to the impact of the flow on the blades with straight profiles, these fans have relatively low efficiency [4]. ...
... The performance of the fan depends on, in addition to the basic geometry of the fan, the shape of the blade profile and the position of the blade [4][5][6]. ...
... Flow characteristics in the region of the trailing edge of the profile determine lift [4]. The shape of the profile was determined after a series of numerical simulations of flow in these fans with different angles of the profile end curvature [1]. ...
Article
Full-text available
Reversible axial fans are used to achieve air (gas) flow in both directions. An axial fan only has an impeller that can achieve the reverse flow by changing the direction of the impeller rotation. In order to obtain the same performance for both directions, the profiles of the impeller blades should be completely symmetrical, in the shape of the ellipse. This paper presents the design and performance for a reversible axial fan with blades that have a slightly doubly curved profile. The shape of the profile, whose design is shown here, was previously obtained on the basis of the numerical simulation in the profile cascade. For the experimental tests, an axial reversible fan model with double curved profiles of the blades was made. Fan performance was obtained by testing a fan for three blade positions on a standard test installation. The performance curves were compared with the performance of the reversible axial fan blades with straight profiles. The fan with doubly curved profile blades achieved a greater increase in pressure and flow than the fan with straight profiles, with approximately the same efficiency. Low pressure axial reversible fans are used in drying chambers for wood and such a design can achieve higher drying efficiency.
... The focus of research on fan aerodynamic design is therefore moving away from the classic basic design methods that were widely adopted before the development of reliable CFD tools for the design process. A comprehensive review of axial-fan design up to the 1970 is given in Ref. [4], whereas an informative account of state of the art of axial-fan design before the end of the last millennium can be found in Ref. [5]. ...
... These charts were obtained from the application of a mean-line model conceived to estimate the aeraulic efficiency of tube-axial fans having blade load in agreement with the constant swirl distribution at the rotor exit. The mean-line model is based on a theoretical analysis of fan performance and energy losses in annular cascades, inspired by that suggested by Wallis [5] for free vortex design fans. The previous work of the current authors [15] also reports the detailed description of the model and its experimental validation. ...
... The design of the USW28 blading is the result of a two-step method that works without any CFD support. The first step (step I, in the following) leads to an intermediate blade by means of a reduced version of the "quasi-2D" design method for nonfree-vortex blades originally conceived by Kahane [23], then adapted to axial fans by Wallis [5] and, finally, formalized in Ref. [16] with the name "Kahane-Wallis method." The second step (step II, in the following) generates the improved blade using a simplified version of the "quasi-3D" step, named "Q3D" in the forward-swept blades design method suggested by Vad [6]. ...
Article
This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high-efficiency industrial fans. To this end, the method has been applied to a 315mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560mm industrial fan.
... However, design examples and theoretical discussions lead to the conclusion that he agrees with using high-Re polars in the range of Reynolds numbers covered by axialfans blading. Finally, Wallis [15] takes the critical Re values, measured in the available tests on low-speed compressor blading (e.g., [16]), as critical values also for axial-fan blading. However, in absence of low Reynolds aerofoil data, he suggests to preliminarily disregard Reynolds effects on polar data [17], and consider them in a second instance, using a correlation to increase the aerofoil drag coefficient. ...
... However, in absence of low Reynolds aerofoil data, he suggests to preliminarily disregard Reynolds effects on polar data [17], and consider them in a second instance, using a correlation to increase the aerofoil drag coefficient. Wallis also suggests the introduction of additional nose droop to blade sections, which increases from 1% to 3%, as Reynolds number decreases from the value of 3x10 5 [15]. ...
... In addition, the hub-totip ratio of this machine is higher than the hub-to-tip ratio of the few PRS fan examples reported in the literature (e.g. [15]). These occurrences justify a shift of the behaviour of this PRS stage towards the RS configuration, which should be higher than that expected for the PRS configuration of actual fans. ...
Conference Paper
Uncertainties surrounding the influence of Reynolds number on the performance of air handling turbomachines are as old as the study of turbomachinery fluid dynamics. In particular, all low-speed turbomachines and most axial-flow fans feature Reynolds numbers that are often lower than the critical value, above which the literature states a limited dependency of blades cascade aerodynamics on Reynolds number. Testing standards already account for this well-known issue, which arises mainly in the case of geometrically similar fans of different size and/or operating conditions. On the other hand, one of the main practical issues in the design of low-speed machines is the disagreement among the most authoritative sources on the value of the critical Reynolds number for axial fans. The many definitions of Reynolds number, which are suited to either fan design purposes or fan performance assessment, introduce additional problems, as the corresponding values may differ by orders of magnitude depending on the chosen definition. A less debated issue deals with the effect of Reynolds number on global performance and efficiency parameters for different axial-flow fan configurations. This paper reports pressure and efficiency data measured at several rotational speeds of four axial fans that feature different configurations, hub-to-tip ratios, sizes and surface finishes. In particular, the tests consider two 315mm and one 630mm tube-axial fans, and one 800mm vane-axial fan with preswirler blading. Data on two vane-axial fans with straightener, and one preswirler-rotor-stator stage, available in the literature, widen the discussion on the Reynolds number effect on the entire category of single-stage axial fans.
... According to Walter et al. [3], a stator blade row will reduce the circumferential component of the dynamic pressure. Wallis [4] states that a diffuser will, as a result of the increase in radial dimension, reduce both the axial and circumferential components due to the conservation of mass and angular momentum, respectively. ...
... The stator row at the outlet of the M-fan had nine blades and a mean chord length of 1.286 m. It was located at a half mean stator chord length downstream of the M-fan, as recommended by Wallis [4]. This stator was capable of removing all the swirl exiting the M-fan. ...
Article
Full-text available
This study investigates the potential gain in operating volume flow rate and static efficiency for an induced draught fan arrangement by reducing the outlet kinetic energy loss. The reduction is achieved through pressure recovery, which is the conversion of dynamic pressure into static pressure. Downstream diffusers, stator blade rows, or a combination of these can recover pressure. Six difference discharge configurations are tested for a fan. An annular diffuser with equiangular walls at an angle of 22° from the axial direction and a length equal to the fan diameter recovers the most pressure over a range of volume flow rates.
... Eck [2], on the other hand, argues that it is impossible to provide exact rules for diffuser diffusion angles: Although half-wall angles in the range of 7° < θ < 9° are often recommend, better diffuser performance might be obtained within the wider range of 5° < θ < 20°, depending on the Reynolds number and turbulence quantities. Diffuser design charts with recommended diffusion angles exist: Wallis [3] provides charts for two-dimensional, conical, and annular diffusers. McDonald and Fox [4] provide a chart for conical diffusers, and Sovran and Klomp [5] provide one for annular diffusers. ...
... Furthermore, it is generally accepted that modest levels of swirl at the inlet of a diffuser can be beneficial for its performance [3]. That is because swirl energizes the nearwall flow, delaying the onset of stall. ...
Article
Full-text available
This study illustrates that downstream diffusers can significantly aid the performance of an induced draught axial flow fan. Two conical diffusers of length 0.2 and 0.4 times the fan diameter and an annular diffuser with a length equal to the fan diameter are tested. At the design flow rate of the fan, the short conical diffuser increases the available static pressure by 17.6% and the static efficiency by 8.9%. The medium-length conical diffuser increases it by 21.9% and 11.7%, respectively. The long annular diffuser produces a 28.2% pressure increase and a 14.2% efficiency increase. The paper also compares the obtained pressure recovery coefficients of the different discharge diffusers using two-dimensional axisymmetric and three-dimensional computations. It shows that the pressure at the outlet of the fan cannot be assumed to be equal to atmospheric pressure, as is prescribed by the fan testing standards. A new method of measuring pressure recovery from two-dimensional computations is proposed.
... A nine-bladed stator row with the blade angle and chord length distributions in figure 4 was capable of removing all the swirl exiting the M-fan at the design flow rate. As recommended by Wallis [15], the stator was located at a half mean rotor chord length downstream of the fan. ...
... which implies that s,dif,o ≈ ∞ . Substituting equations (11) to (15) into equation (10) and rearranging yields the draught equation that was given in equation (1). ...
Article
Full-text available
This study investigates the potential gains in operating volume flow rate and static efficiency of an induced draught axial flow fan system. These gains are achieved through pressure recovery, i.e. the conversion of dynamic pressure at the fan exit into static pressure. Pressure recovery is achieved using downstream diffusers, stator blade rows, and combinations of these. Three different diffuser lengths are considered. Of the shortest diffusers, a conical diffuser increases the operating volume flow rate by 3.2 % and the fan static efficiency by 9.8 % (absolute). A longer conical diffuser increases it by 3.9 % and 11.9 %, respectively. Of the longest diffusers, an annular diffuser increases the flow rate by 5.5 % and the fan static efficiency by 16.8 %.
... Although it is well documented that conical diffusers can enhance fan performance in induced draught ACCs [1,8], there is a void in the literature regarding the extent of these performance improvements. Bekker et al. [6] also pointed out that diffuser design charts are often inappropriately used in combination with axial flow fans to predict fan-diffuser performance. ...
... Downstream stator blade rows and diffusers are capable of pressure recovery [1,2]. Walter et al. [3] theoretically illustrated that the use of a downstream stator blade row could increase the static efficiency of a typical axial flow fan by 7%. ...
Article
This research aims to enhance the performance of a 20-fan induced draught air-cooled condenser (ACC) by increasing the airflow rate and heat rejection rate of the ACC. These improvements are achieved through pressure recovery, which is the conversion of the dynamic pressure loss at the fan outlets into static pressure. Two different conical diffusers are attached to the outlets of the ACC’s fans to facilitate pressure recovery. The shorter diffuser has a length equal to 20 % of the fan diameter and an included angle of 2θ=40°; the longer diffuser is 40 % the length of the fan diameter with 2θ=32°. The performance of this five-by-four ACC is analysed with and without these diffusers through numerical simulation in OpenFOAM. The analysis is performed under windless and windy conditions. The added diffusers increase the volumetric and thermal effectiveness of the ACC by 2.5 % and 2.0 %, respectively, under windless conditions. At wind speeds of 3, 6 and 9 m/s, the gain in volumetric effectiveness declines to 1–2 %, while the gain in thermal effectiveness varies in the range of 0–5 %. The longer of the two diffusers yields greater improvements, especially at higher wind speeds.
... Therefore, even a small decrease of fan efficiency, can create large costs of electrical energy. To this day many books and papers on fan designing methods and their performance characteristics have been published [1][2][3][4][5]. Numerous experimental investigations of fan performances, using different measuring techniques, have been carried out, with the objective to improve fan design methods and to increase fan efficiency [6][7][8]. ...
... It is shown [1][2][3][4][5] that, for ρ ≈ const., the fan efficiency is equal to the product: ...
Article
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Performance characteristics of fans are generally provided for the normal temperature and pressure conditions (tI = 20°C, pI = 101.325 kPa, ρ I = 1.2 kg/m3). Very often, fans operate in different air conditions, occasionally at different air temperatures. In these cases, equations obtained by the law of similarity are usually used for recalculation of the fan operating parameters. Increasing the inlet air temperature causes a decrease in the characteristic of Reynolds number, and may lead to efficiency lowering of the fan. There are also some empirical formulas for recalculation of fan efficiency, when operating at different air temperatures. In this paper, the common way for obtaining fan performance for different operating conditions (air temperature changing) is presented. The results, obtained by recalculation of fan parameters using a law of similarity, are compared to numerical simulation results of the axial-flow fan operating with different air temperatures. These results are compared with results obtained by some recommended empirical formulas, as well. This paperwork is limited to low-pressure and mid-pressure fans, which represents the majority of all fans used in practice, for different purposes.
... This paper presents the comparison of the characteristics of the fan with the straight profiles of the blade numerically obtained. We should be careful with the introduction of double curved profiles since any change in the curvature can lead to separation of the flow from the surface of the blade profile and thus to the degradation of the fans' performance [14,15]. ...
... In order to achieve equality of fluid energy exchange along the radius of the impeller, the blades of the impeller are spatially curved. The fan impeller is designed under the principle of equal specific work of all elementary stages, that is, under the principle of the flow along axially symmetrical cylindrical surfaces [3,6,15]. To determine the shape of the fan blades, the profiles are designed in 13 elementary stages, approximately equally distributed along the height of the blade. ...
Article
In reversible axial fans a change in the direction of the impeller rotation is accompanied with a change in the direction of the working fluid flow. To satisfy the flow reversibility, the impeller blades are usually designed with straight symmetrical profiles. The flow reversibility may also be achieved by using asymmetrical blade profiles in which, to satisfy the equality of the leading and trailing angle of the profiles, the mean line of the profile has to have a double curvature in the shape of the stretched letter 'S'. The paper numerically investigates the influence of the doubly curved blade profiles on the reversible axial fan characteristics. Numerical simulations are carried out on an axial fan only with the impeller, with the blades that have double-curved mean line profiles for different values of the angles at the profile ends. For numerical simulation the ANSYS CFX software package is used. Results of the numerical simulation are shown in diagrams Δp(Q), h(Q) and P(Q) at different angles of the profile ends. On the basis of the simulation and analysis of the characteristics, appropriate conclusions are proposed, along with the most advantageous profile of the blades.
... To accommodate acoustic linings and cooling lines a thicker profile is desirable which can be derived from vanes providing close to a constant area turning [12,13] at the corners. The design of axial flow fans for wind tunnel and other applications have been discussed in numerous turbomachinery texts [14][15][16][17][18]. The fan design itself needs to be optimized for specific operational requirements using computational modelling of flow in the blade passage. ...
... A partial section of the tail fairing was truncated at the trailing end of both hybrid and ellipsoidal fairings. As suggested in the literature [18], the truncation of the walls of a diffuser with reduced included angle makes them perform much better compared to a diffuser with higher included angle with the same length. This tail fairing truncation was tested for reducing the tail length while studying the flow in the annular diffuser. ...
Article
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A full scale numerical study of a large low speed closed circuit wind tunnel has been carried out in this work. The paper shows the use of numerical results to improve the design and investigate the internal flow physics inside a wind tunnel circuit, whereas most of the existing wind tunnel designs have relied on analytical guidelines. Using a steady state RANS simulation on full scale wind tunnel, this work identifies regions with undesirable flow and design features causing such effects like test diffuser included angle and fan tail shape. The paper also discusses the lesser known requirements for effective flow simulation of a wind tunnel like roughness in walls, screens and honeycomb as porous boundary and considering fan geometry while solving for detailed flow field. The modelling of internal flow inside a tunnel required grid resolution of complete domain and proper location for domain boundary, i.e. inlet/outlet boundaries for convergence and a realistic flow simulation. This work found that the flow in complete wind tunnel is affected by flow features developing in one region and their interaction with turning, diffusing and contracting flowfields. In this context, the interaction of disintegrating fan tip vortices with centerbody wake is highlighted. The pressure drop calculation at various mass flow rates has been used to derive the energy ratio of the tunnel and the required performance characteristics of the fan. The CFD results were used to iteratively optimise the deisgn by modifying its components and ends up achieving a overall higher flow quality and lower energy ratio. The energy ratio of 3.2 was achieved for test jet speed of 70 m/s with 2.52 m2 cross-sectional area. The methodology presented in this paper for setting up wind tunnel numerical domain and numerical investigation of flow field to assist in wind tunnel design will give useful guideline for designers of such wind tunnel in future.
... Eck (1973) defined various fan geometric parameters and carried out a series of systematic analyses that enables to evaluate fan performance. Later, Wallis (1983) developed a combined theory for airflow through the fan and duct design. Bleier (1998) studied the concepts explained by Wallis (1983) and performed calculations to make the preset requirements in volumetric flow rate, static pressure, power, and efficiency. ...
... Later, Wallis (1983) developed a combined theory for airflow through the fan and duct design. Bleier (1998) studied the concepts explained by Wallis (1983) and performed calculations to make the preset requirements in volumetric flow rate, static pressure, power, and efficiency. ...
Article
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This paper presents the numerical analysis of three types of magnesium-based, axial-flow automotive cooling fans. The numerical modeling is conducted for geometrically modified fan designs with and without bead structure. The effect of geometric modifications of the fan blades on the fan performances (P-Q curve), fan efficiency, and energy efficiency is investigated using unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the sliding mesh methodology. The baseline fan having no-beads is fabricated using 3D printing technology and tested to measure the flow velocity and volumetric flow rate which shows good agreement to the numerical results. Subsequently, fans with beads are further optimized to achieve a significant increase in fan performances. To investigate the fan vibrations, modal analysis is also carried out using magnesium-alloy AZ31 as the fan material. The modal analysis gives natural frequencies of all types of fans which are beyond the fan rotational frequency and seems satisfactory.
... According to Miller (1971: 84), wideangled diffusers with free-discharge outlet conditions having half-wall angles larger than six degrees and area ratios larger than two, benefit most from swirl. Wallis (1983), on the other hand, states that the benefits of swirl are scant and often countered by the losses associated with it-such as a higher outlet dynamic pressure loss. He concedes that it is generally accepted that swirl angles up to ten degrees may prove beneficial. ...
... Discharge diffusers, stator blade rows, and combinations thereof are capable of achieving pressure recovery. Therefore, these discharge configurations can enhance the performance of axial flow fans in an induced draught arrangement (Eck, 1973;Wallis, 1983;McKenzie, 1997;Kröger, 1998). However, the literature does not provide clear guidelines as to which diffuser configuration (conical or annular) would be best, how long the diffuser should be, or which wall angles would prove most effective. ...
Thesis
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This study aims to enhance the performance of an induced draught air-cooled condenser (ACC) by increasing the ACC's air mass flow rate and heat rejection rate. These improvements are achieved through pressure recovery, which is the conversion of the dynamic pressure at the fan outlets into static pressure. Pressure recovery increases the effective static pressure rise of the axial flow fans in the ACC, resulting in a higher operating airflow rate. Consequently, higher heat removal rates are possible. Stator blade rows and diffusers are capable of pressure recovery. Combinations hereof are tested for the axial flow fan featured in the ACC (i.e. the M-fan) through numerical simulation in OpenFOAM. Diffuser lengths of l_dif = d_F, 0.4d_F and 0.2d_F are considered, where d_F = 7.315 m is the fan diameter. The most promising discharge configurations are selected for a five-by-four induced draught ACC. The ACC is then analysed with and without these appendages under windless and windy conditions. Wind directed along the shorter and longer axes of the ACC is considered at wind speeds of 3, 6 and 9 m/s. Amongst the diffusers of length l_dif = d_F, an annular diffuser with both walls diverging at 22° from the axial direction recovers the most pressure for the M-fan over a range of flow rates. For the l_dif = 0.4d_F length, a conical diffuser with an included angle of 2θ = 32° recovers the most pressure. And a conical diffuser with 2θ = 40° yields the highest pressure recoveries for the l_dif = 0.2d_F length. However, the l_dif = d_F annular diffuser is deemed impractical for ACC application due to its length and wide wall angles. Under windless conditions, both conical diffusers increase the mass flow rate through the five-by-four ACC by ~2.5 %. As a result, the heat transfer rate improves by 2.0 %. The power consumption of the ACC fans also drops by 5.2--5.5 %, increasing the heat-to-power ratio by 12.4--13.1 W/W. In a light breeze of 3 m/s, the increase in mass flow rate due to the diffusers is 1.7--2.0 %; in a moderate breeze of 6 m/s, the increase is 0.9--1.3 %; and in a fresh breeze of 9 m/s, it is 1.0--1.6 %. There is more variation in the thermal performance results of the ACCs featuring the two different diffusers: The shorter diffuser does not improve the heat transfer rate of the ACC as much as the longer diffuser does under windy conditions. At 6 m/s, the ACC with longer diffusers rejects 1.6--2.2 % more heat than the ACC with shorter diffusers. At 9 m/s, the former rejects ~2.5 % more heat than the latter. This research demonstrates that discharge diffusers can enhance the performance of an induced draught ACC. The diffusers' pressure recovery increases the mass flow rate through the ACC, aiding its heat rejection capability. From a performance perspective, the l_dif = 0.4d_F diffuser is recommended. However, practical considerations might render the shorter l_dif = 0.2d_F diffuser more suitable.
... The design method used to produce the M-fan is based on the work of Bruneau [4] and Van der Spuy [5]. These methods draw heavily from the works of Wallis [6] and Dixon [7]. The M-fan has been tested numerically at design scale by means of a modified version of the Actuator Disk Model (ADM) of Thiart and von Backström [8] as well as a periodic three dimensional CFD model. ...
... The CFD data is shown to correlate reasonably with the experimental data, especially at the design point. The effect of 6 Copyright © 2018 ASME the tip gap on total-to-static efficiency is more severe in the CFD data. On average total-to-static efficiency is reduced by approximately 2% for every 2 mm increase in tip gap in the experimental data, whereas the reduction in efficiency estimated by the numerical data is in the order of 7% near the operating point. ...
Conference Paper
An axial flow fan developed in previous study is tested in order to characterise its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary CFD results obtained using an actuator disk model as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4 % and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the BS 848 (ISO 5801) type A fan test facility at Stellenbosch University. A RANS CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicates that the M-fan does not meet the pressure requirement set out in the initial study, at the design blade setting angle of 34 degrees. Under these conditions the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.
... In these methods, both the specific work of the rotor, Y pá , and meridional velocity, c m , are no longer constant along the length of the rotor blades. In this paper is used, a type of non-free vortex adopted by Wallis (1993), where the circumferential component of the absolute velocity after rotor, c u6 , varies linearly along the blade. This condition is represented of dimensionless form by Eq. (8). ...
... The approximate solution of the equation of momentum along the blade, considering that no swirl of the flow at the inlet of the rotor (pre-rotation), that is, the circumferential component of the absolute velocity at the inlet, c u3 = 0, Fig. 1, can be obtained by (Wallis, 1993): ...
Article
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The main feature of a Reversible jet fan is to provide the same air flow and thrust in both directions of flow, keeping the maximum ratio thrust-power in any range of electrical motor power. These conditions could be achieved with the use of a rotor formed by double-symmetric airfoils, for example, an elliptical airfoil. This paper present a rotor blade design of a reversible axial rotor of a jet fan usually used for ventilation of road tunnels, the design is based on a methodology that utilizes a non-free vortex condition for resolving the radial equilibrium equation. This project was developed with reference in certain data available in the literature of elliptical profiles arranged in linear cascades representing axial rotors, gotten by means of computational fluid dynamics tools. Moreover, the aerodynamic performance characteristics of the reversible axial rotor were found either in the design point or out of this for a specific rotation using Computational Fluid Dynamics Methods (CFD) by means of the commercial software Fluent®. With numerical simulation results is possible to plot the aerodynamic performance curves, total pressure, thrust and fan’s shaft power which show good agreement respect to the design data.
... Pedestal and table fans are widely used to produce a comfortable environment in enclosed spaces. There are different brands of fans available in the market with various blade shapes, sizes and number of blades as well as different levels of performances [1]. Globally there is an increasing effort to improve the energy efficiency of appliances as an effective mitigation option in responding to the growing energy and environment issues [3].Initially a testing procedure was developed in order to conduct the performance analysis of pedestal and table fans. ...
Conference Paper
Full-text available
The pedestal and table fans are widely used to provide air mixing and comfort region in enclosed spaces. There are different brand of fans with various blade shapes, sizes and number of blades which lead to different level of performances. Aerodynamic characteristic is one of the important aspect which affects the fan performance. Performance of four different type of fans were analysed through the experimental measurements of velocity distribution, power consumption and angular velocity. A test rig was constructed with suitable instrumentation and integrated using a computerised data acquisition platform to acquire axial flow velocity measurements at each plane. The velocity distribution was measured at sufficient number of planes with different regulator position of the fan. Key parameters such as the flow rate, kinetic energy, linear momentum and the jet diameter were calculated from the experimental data. Different velocity distributions were obtained for different type of fans in the analysis of the data. Iso-velocity lines were obtained to analyse the spread of the velocity. Results show that the velocity profiles of the fans depend on the regulator position and blade parameters such as blade shape and material. It is also found that the overall energy efficiency of the fan depends on the angular velocity for different regulator positions. Further the incremental flow rate was also calculated to analyse the percentile change in flow rate for each regulator position. The impact on the performance when the fan was set to oscillate is also discussed in this paper. The results of the present study indicate the complexity of the influence of various parameters on the performance of the fan such as blade shape, angular velocity and power consumption and the necessity of a detailed experimental analysis of the velocity distribution of the fan for performance analysis.
... In the aerodynamic design of axial fan, the free vortex design method and the arbitrary vortex method are two widely used methods, and both require the assumption of twodimensional flow. The free vortex method is widely used in the design of axial fan which satisfactorily meets the design requirements of low speed wind tunnel, mine ventilation system, and cooling system, and the details of this method have been described by Collar [2], Pope [3] and Wallis [4]. This method also assumes that the flow velocity has no radial component, and the theoretical axial velocity and the total pressure rise of the fan are both constant along the fan radius. ...
... There are empirical methods to select most of the fan geometrical parameters based on the performance requirements [1][2][3][4]. Blade is built by stacking of the airfoil layers on radial sections (preferably at the centroid) and lofting through them to get a CAD geometry [5] using any of the turbomachinery packages. There are controls to manipulate the blade geometry. ...
Conference Paper
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A large diameter, low speed axial flow fan has been designed to drive the Centre for Railway Research (CRR) wind tunnel at IIT Kharagpur. Total pressure rise of 1400 Pa is required from the fan at the design mass flow rate of 420 kg/s. The outer diameter of the fan is 4 m with 0.6 hub to tip ratio. The present paper discusses the design methodology and computational analysis of wind tunnel fan. The design methodology includes a preliminary mean line analysis using the fundamental governing equations and CFX inbuilt design module. Subsequently, detailed computational analysis of the rotors was carried out using ANSYS CFX ®. Based on the results obtained from the CFX analysis, the mean line analysis was modified to achieve the desired performance of the rotor. Parametric study was undertaken with different blade number combination, axial spacing, blade chord length, location of maximum thickness, leading edge profile, etc. The selection of number of blades for rotor and stator is an important aspect for such fan design in terms of cost, utility installation and noise. For low background noise in wind tunnel higher number of blades with suitable combination was selected for the fan ensuring the tone noise (produced by interaction of rotor and stator) is generated at attenuable frequencies. The blade angles, chord lengths, blade camber were optimized for good aerodynamic performance in terms of blade loading, wake thickness, hub-tip pressure profile, overall efficiency and pressure rise. It is strongly believed that discussed design aspects in terms of selection of various geometrical parameters for wind tunnel fan will give useful guidelines for future design of a low speed, large diameter fan of such capacity.
... Wallis (1968) deduced an algorithm for predicting deviation angle and the axial fan design. Downie et al. (1993), Wallis (1983) and Wallis (1961) studied the performance of axial fans experimentally and theoretically. Bruneau (1994) deduced a simple design approach, which was the foundation for many other studies that used his algorithm and verified it. ...
... There are empirical methods to select most of the fan geometrical parameters based on the performance requirements [1][2][3][4]. Blade is built by stacking of the airfoil layers on radial sections (preferably at the centroid) and lofting through them to get a CAD geometry [5] using any of the turbomachinery packages. There are controls to manipulate the blade geometry. ...
Conference Paper
A large diameter, low speed axial flow fan has been designed to drive the Centre for Railway Research (CRR) wind tunnel at IIT Kharagpur. Total pressure rise of 1400 Pa is required from the fan at the design mass flow rate of 420 kg/s. The outer diameter of the fan is 4 m with 0.6 hub to tip ratio. The present paper discusses the design methodology and computational analysis of wind tunnel fan. The design methodology includes a preliminary mean line analysis using the fundamental governing equations and CFX inbuilt design module. Subsequently, detailed computational analysis of the rotors was carried out using ANSYS CFX ®. Based on the results obtained from the CFX analysis, the mean line analysis was modified to achieve the desired performance of the rotor. Parametric study was undertaken with different blade number combination, axial spacing, blade chord length, location of maximum thickness, leading edge profile, etc. The selection of number of blades for rotor and stator is an important aspect for such fan design in terms of cost, utility installation and noise. For low background noise in wind tunnel higher number of blades with suitable combination was selected for the fan ensuring the tone noise (produced by interaction of rotor and stator) is generated at attenuable frequencies. The blade angles, chord lengths, blade camber were optimized for good aerodynamic performance in terms of blade loading, wake thickness, hub-tip pressure profile, overall efficiency and pressure rise. It is strongly believed that discussed design aspects in terms of selection of various geometrical parameters for wind tunnel fan will give useful guidelines for future design of a low speed, large diameter fan of such capacity.
... The design method used to produce the M-fan is based on the work of Bruneau [4] and Van der Spuy [5]. These methods draw heavily from the works of Wallis [6] and Dixon [7]. The M-fan has been tested numerically at design scale by means of a modified version of the Actuator Disk Model (ADM) of Thiart and von Backström [8] as well as a periodic three dimensional CFD model. ...
Conference Paper
An axial flow fan developed in previous study is tested in order to characterise its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary CFD results obtained using an actuator disk model as well as a periodic three dimensional model indicate that the fan meets the specified performance targets , with an expected total-to-static efficiency of 59.4 % and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the BS 848 (ISO 5801) type A fan test facility at Stellenbosch University. A RANS CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicates that the M-fan does not meet the pressure requirement set out in the initial study, at the design blade setting angle of 34 degrees. Under these conditions the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application , however it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance , potentially improving performance at low flow rates. NOMENCLATURE Symbols A Area [m 2 ] d Diameter [m] N Rotational speed [RPM] P Power [W] P Normalised power [W] p Pressure [Pa] T Torque [Nm] ˙ V Volume flow rate [m 3 /s] αε Bellmouth calibration constant ∆ Change in a generic property 1 Copyright c 2018 by ASME η ts Total-to-static efficiency ρ Density [kg/m 3 ] Subscripts atm Atmospheric d Dynamic F Fan plen Plenum chamber t Total s Static Superscripts Normalised INTRODUCTION Axial flow fans are used to move air through heat exchan-ger bundles allowing heat transfer to take place. Air-cooled heat exchangers typically make use of arrays of axial flow fans which can result distorted inflow conditions, even under normal operation. Wind, site layout and other ambient effects may also further reduce fan performance [1]. As part of the MinWaterCSP project [2], Wilkinson et al [3] developed the M-fan, which was designed to perform well under the challenging operating conditions encountered by axial flow fans in air cooled heat exchan-gers. The performance of the M-fan was investigated using both simplified and explicit CFD modelling [3], however the performance of the fan was not experimentally investigated. This study experimentally evaluates the performance of the M-fan under a range of different operating conditions. The results of the experiments are used to validate the CFD models used in the previous study as well as to provide insight into the effect of tip clearance, blade angle and hub configuration on fan performance. The design method used to produce the M-fan is based on the work of Bruneau [4] and Van der Spuy [5]. These methods draw heavily from the works of Wallis [6] and Dixon [7]. The M-fan has been tested numerically at design scale by means of a modified version of the Actuator Disk Model (ADM) of Thiart and von Backström [8] as well as a periodic three dimensional CFD model. Simulations run in ANSYS FLUENT 17.2 indicate that the fan performs satisfactorily attaining a total-to-static pressure rise of 114.7 Pa and a total-to-static efficiency of 59.4 % at the design point, 333 m 3 /s. However these simulations were only run over a small range of flow rates near the design point and the performance of the fan across the full range of flow rates is not known. Additionally the numerical models used to assess the fans performance have not been validated, deeming experimental testing of the M-fan necessary. The M-fan is designed as a 24 ft (7.3152 m) diameter fan, however since no test facility of this size is available, a scale model is tested on the 1.542 m
... From the results presented here, 3-and 5-blade propellers appear to be the least annoying of those tested. It is likely this stems from the basic low-noise fan-design principle of having different prime numbers of rotors and stators as a noise reduction method [19]. This results in lower fluctuation strength and loudness when compared with similar propellers of different blade numbers. ...
Conference Paper
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Increasingly, operations with unmanned aircraft systems (UAS) are occurring in populous regions. Commercial entities propose increasingly frequent, very low-level flights of a diverse range of small craft (particularly quadrotors) in urban environments. There is a significant body of research addressing safety, security, and privacy issues for UAS and an even greater amount dedicated to manned craft. However, our review reveals relatively little available information on the characteristics of UAS noise sources, factors influencing propagation, the people impacted and the psychoacoustic factors influencing their response. This work begins to analyse the problem by investigating the effect of quadrotor propeller-blade numbers on acoustic annoyance. Frequency spectra for each propeller type are compared against that for a DJI Phantom 4. The effect on loudness, sharpness, and fluctuation strength is also discussed. A number of technical mitigation measures are hypothesised, including flight path planning for reduced exposure, and legislative restrictions. Propeller designs taking inspiration from low noise fans are recommended as a method of reducing the acoustic impact of routine UAS operations over populous areas.
... Circular arc blading is particularly suitable for highpressure rise units. Flat under the surface building is more appropriate for low-pressure rise units as shown in [49]. Constant thickness blades, used commonly for mixed flow fans and blowers, are not often used for high-performance vane axial fans in aircraft applications. ...
Article
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This study presents a custom guide vane design to substantially reduce the waste energy in axial fans. Ideally, there is no velocity component in the radial direction in axial fans, but in practice, the air leaving the axial fan has a large tangential component of velocity which produces a large amount of swirl kinetic energy. In order to solve this problem, a guide vane is designed to remove the rotational component of the air. The methodology described in this project is based on the fundamental governing continuity, momentum, and energy equations using the Finite Volume Method (FVM). In this project, the standard k-ω model is used for turbulent modeling. Two dimensional (2D) geometry of blades and airflow cross-section are designed using AutoCAD and CATIA while GAMBIT is employed to generate a suitable mesh for the three dimensional (3D) model. The mesh independence test is done to analyze the performance. The axial fan is simulated using FLUENT software to prove an increase in airflow rate after using the guide vane. Considering the final results, it can be observed that the airflow is increased up to 6.3%.
... The design method used to produce the M-fan is based on the work of Bruneau [4] and Van der Spuy [5]. These methods draw heavily from the works of Wallis [6] and Dixon [7]. The M-fan has been tested numerically at design scale by means of a modified version of the actuator disk model (ADM) of Thiart and von Backstr€ om [8] as well as a periodic three-dimensional CFD model. ...
Article
An axial flow fan developed in previous study is tested in order to characterise its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary CFD results indicate that the fan meets the specified performance targets. Several fan configurations are tested experimentally in order to ascertain the effect of tip clearance, blade angle and hub configuration on fan performance. A scaled 1.542 m diameter model of the M-fan is tested on an ISO 5801 type A fan test facility. A RANS CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. Experimental data indicates that the M-fan does not meet the pressure requirement set out in the initial study, at the design blade setting angle. Increasing the blade angle is shown to improve the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap effects, however tip losses are also shown to be overestimated by the CFD simulations. Results indicate that the M-fan is suited to its intended application, however its opperating configuration should be adjusted. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.
... 15 Log-Tchebycheff metodu ile hız-alan taraması ...
Thesis
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RÜZGAR TÜNELİ VE VE VE VE AKIŞ GÖRÜNTÜLEME TEKNİKLERİ Wind Tunnel And Flow Visualization Techniques
... This work will use a type of non-free vortex based on Wallis (1983) and Sarmiento et al. (2017) ...
Article
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The sound generated by axial flow fans has become increasingly important in several industrial areas. These devices represent considerable noise sources that must be considered from the design stage. The scope of this research work is to present an axial fan design methodology based on the theory of the wing lift and to compare the aerodynamic and aeroacoustics behavior with the free vortex and the non-free vortex conditions. The effect of forward circumferential sweep on the rotor blades is analyzed in both conditions, which consists of a displacement in the tangential direction in the direction of rotor rotation. A cubic polynomial function is proposed for the construction of the blade geometry with circumferential sweep. It defines the center line of the blade and it is taken at 50% of the leading edge of each blade profile. The methodology for analyzing aeroacoustics behavior in fans is based on the integration of Computational Aeroacoustics and Computational Fluid Dynamics in order to analyze aerodynamic behavior, sound power level and sound pressure level at the preliminary design stage. It was verified that although both rotors present a similar aerodynamic behavior (the NFV rotor has a slightly lower performance), according to the analysis of local sound sources, the NFV rotor presents a slight decrease in the sound sources. It was also verified that the NFV rotor presents 2.2 dB less in sound pressure level than the FV rotor.
... Detailed flow measurement and computation were performed for outlet flow field for investigating the responsible flow mechanisms. The results show the forward-skewed blade can cause a span wise redistribution of flow toward the blade mid-span and reduce tip loading [21][22][23][24][25][26][27][28][29][30][31][32]. ...
... 2) Gaz de décoration de l'aspirateur, fours, fonderie. simple pour le calcul de la distribution du flux méridional, qui avait été initialement présenté par Wallis dans la troisième édition de son livre [24]. Il est remarquable que la méthode de Wallis soit en fait le développement des équations présentées par Ruden [25]et Kahane [26] environ 50 ans auparavant. ...
Thesis
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Centrifugal fans are machines for moving a gas, such as air, by accelerating it radially outward in an impeller towards a surrounding casing. They are often used in heating and ventilation and air conditioning (HVAC) systems. But, the efficiency of the fan can be further improved by studying their detailed performance characteristics and modifying their geometry. Beyond its design point, the fan's performance begins to drop. In this context, a numerical simulation with the aim of predicting the flow field which passes through two axial fans in a tunnel or cage which contains electronic components has been carried out. The flow is three-dimensional and turbulent, such as can be encountered in the suction and bulge of air. The CFD Fluent code based on the finite volume method was used for turbulent flow using the k-ε model and the model. Our numerical simulations were presented in two different cases: with and without heat transfer. The results obtained our allowed a better understanding of the phenomenology of the flow in question, in particular the improvement of heat transfer by air discharge in chambers or tunnels contain components. Keywords: centrifuge fans, turbulent flow, CFD, performanc
... The hub is a much overlooked aspect when specifying the configuration of an axial flow fan. Smooth, bulb-shaped hubs are typically analysed and recommended [2] due to the superior performance of fans utilising such a hub. However, with a 3 m diameter, such a hub configuration would be impractical and will increase the cost of an ACC installation. ...
Conference Paper
Axial flow fans used in air-cooled condensers are typically analysed with smooth rounded hubs as they offer superior performance when compared to other hub configurations. However, such a hub configuration is impractical and may increase the manufacturing and installation costs of air-cooled condensers. As such, it is desirable to use a simpler, yet effective, hub configuration in order to reduce the installation cost. This paper assesses the impact that a simpler hub configuration may have on the performance of an axial flow fan. This is done through a comparison of three hub configurations: a cylindrical hub with a flat nose, a cylindrical hub with a hemispherical nose, and a disk hub, installed on the B2a-fan. Computational fluid dynamics modelling, utilising OpenFOAM, is used to simulate each hub configuration. It is found that the impact on performance due to hub configuration is dependent on the volumetric flow rate through the fan. A thin disk hub exhibits superior performance at low flow rates, resulting in a 8.4% improvement in total-to-static pressure rise and a 5.7% point improvement in total-to-static efficiency. As volumetric flow rate increases, the effectiveness of the disk hub configuration reduces while the hemispherical and flat nosed cylindrical hub configurations result in similar performance metrics at the design point flow rate. At above design point flow rate, the flat nosed cylindrical hub configuration shows an improvement in performance over the hemispherical nose cylindrical hub configuration, with a 9.5% increase in total-to-static pressure rise and a 5.1% point improvement in total-to-static efficiency.
Article
Effects of the inlet guide vanes on the static characteristics, aerodynamic noise and internal flow characteristics of a small axial flow fan are studied in this work. The inlet guide vanes with different outlet angle are designed, which are mounted on the casing and located at the upstream of the impeller of the prototype fan. Both steady and unsteady flow simulations are performed. The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model, while the unsteady flow is computed with large eddy simulation. According to the theoretical analysis, the inlet guide vanes with outlet angle of 60° are regarded as the optimal inlet guide vanes. The static characteristic experiment is carried out in a standard test rig and the aerodynamic noise is tested in a semi-anechoic room. Then, performances of the fan with optimal inlet guide vanes are compared with those of the prototype fan. The results show that there is reasonable agreement between the simulation results and the experimental data. It is found that the static characteristics of small axial flow fan is improved obviously after installing the optimal inlet guide vanes. Meanwhile, the optimal inlet guide vanes have effect on reducing noise at the near field, but have little effect on the noise at the far field. © 2017, Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature.
Conference Paper
The performance of large mechanical draft air-cooled heat exchangers is directly related to fan performance which is influenced by atmospheric wind conditions, as well as the plant layout. It is often necessary to numerically model the entire system, including fans, under a variety of operating conditions. Full three-dimensional, numerical models of axial flow fans are computationally expensive to solve. Simplified models that accurately predict fan performance at a lesser expense are therefore required. One such simplified model is the actuator disk model (ADM). This model approximates the fan as a disk where the forces generated by the blades are calculated and translated into momentum sources. This model has been proven to give good results near and above the design flow rate of a fan, but not at low flow rates. In order to address this problem two modifications were proposed, namely the extended actuator disk model (EADM) and the reverse engineered empirical actuator disk model (REEADM). The three models are presented and evaluated in this paper using ANSYS FLUENT. The models are simulated at different flow rates representing an axial flow fan test facility. The resulting performance results and velocity fields are compared to each other and to previously simulated three dimensional numerical results, indicating the accuracy of each method. The results show that the REEADM gives the best correlation with experimental performance results at design conditions (ϕ = 0.168) while the EADM gives the best correlation at low flow rates. A comparison of the velocity profiles shows that none of the three models predict the radial velocity distribution at low flow rates correctly, however the correlation improves at flow rates above ϕ = 0.105. In general the upstream velocity profiles, where reversed flow occurs through the fan, are poorly predicted at low flow rates. At the flow rates above ϕ = 0.137 the correlation between the velocity profiles for the simplified modes and the three dimensional results is good.
Book
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Las grandes civilizaciones nacieron a orillas de los ríos, El Indo, en la india, el río amarillo en China, entre el Tígris y el Eufrates en medio oriente, y en el valle del Nilo en África. Todas ellas, aprendieron a utilizar las crecidas de los ríos canalizando el agua para ampliar las áreas cultivables. Los Chinos inventaron las primeras exclusas con el fin de permitir a los juncos remontar los ríos, crearon las primeras bombas de agua de accionamiento humano. Los jardines colgantes de Babilonia fueron una enorme obra de Ingeniería Hidráulica, el agua se canalizaba y elevaba para regar los diferentes niveles. La cultura griega realiza enormes avances en lo que a máquinas hidráulicas se refiere, Herón de Alejandría (? s I dC) inventa una bomba de pistones accionada manualmente y que es utilizada como bomba contra incendios, crea la primera turbina hidráulica accionada por vapor, aunque en aquel momento se utilizó casi exclusivamente para divertimento y asombro de las gentes, la única aplicación conocida fue su utilización para abrir las puertas de un templo griego. Las ruedas hidráulicas fueron ampliamente utilizadas en la antigua Grecia para accionar ruedas de molinos, las ruedas de cangilones y el tornillo de Arquímedes de Siracusa (287-212 aC) fueron extensamente utilizados para elevar agua. Arquímedes es asimismo recordado en la actualidad por su famoso principio, el cual elaboro para determinar si la corona de oro del rey Hierón II de Siracusa estaba en realidad hecha de este material. En la actualidad se sigue utilizando el tornillo de Arquímedes. En casi 2000 años no aparece prácticamente ningún descubrimiento sustancial en lo que a máquinas hidráulicas se refiere, tanto la cultura romana como las civilizaciones India y China únicamente rentabilizan las invenciones realizadas por civilizaciones precedentes. Únicamente en el siglo XI aparecen en europa central, Alemania, los primeros molinos de viento, los cuales permanecen prácticamente invariables hasta la revolución industrial del siglo XVIII. A partir de la aparición de la máquina de vapor, descrita por Govanni Battista (1601), y también por Edward Sommerset (1663), y que Herón inventó, las máquinas hidráulicas dejan atrás su largo periodo de aletargamiento, en (1690) Denis Papin propone la obtención de trabajo mecánico a partir de una máquina de vapor, y en (1698) Thomas Savery utiliza una máquina de vapor para bombear agua de una mina, el tipo de bombas que se utilizaban eran las bombas de pistones. Hasta el siglo XIX no aparecen las turbinas hidráulicas, así por ejemplo, la turbina Pelton o turbina de acción, es desarrollada por Allen Pelton (1829-1908) ingeniero americano, posteriormente el ingeniero británico emigrado a los EEUU James Bicheno Francis (1815-1892) crea la turbina Francis, turbina de reacción, al cabo de pocos años Víctor Kaplan (1876-1934) ingeniero austriaco desarrolla una maquina axial que es denominada turbina Kaplan.II Máquinas Hidráulicas problemas El desarrollo de las bombas centrífugas así como las máquinas volumétricas de engranajes y paletas se realiza asimismo a finales del siglo XIX principios del XX. El libro que aquí se presenta se centra en la aplicación de máquinas hidráulicas centrífugas, bombas y ventiladores, aunque bien es cierto que en dos de los apartados del libro, se explora el diseño de dichas máquinas. Los problemas expuestos intentan explicar de una manera llana los conceptos involucrados, con el fin de que el lector inexperto en la materia vaya adentrándose en la nomenclatura y profundizando paulatinamente en los parámetros mas significativos relativos a estas máquinas. En todo momento se ha pretendido seguir la filosofía de Demócrito (460-360 aC), y Sócrates (470-399 aC), “conócete a ti mismo y conocerás a los demás”. Lo que se pretende es que el lector con una mente abierta, por si mismo vaya entendiendo conceptos y profundizando en los mismos. Recordar cabe por otro lado la enseñanza que la historia nos aporta, si Hammurabi (1792-1750 aC) crea la ley del talión, bueno es recordar los postulados de Mohandas Gandhi (1869-1948) al respecto, “si todo el mundo sigue aplicando la ley de ojo por ojo diente por diente, pronto nos vamos a quedar todos ciegos”. Bueno es pues dejar a un lado puntos de vista antiguos para así adentrarse libremente en los nuevos. Aprendamos pues, y aprendamos de nuestros propios errores, y puesto que el lector va a descubrir muchos de ellos en el libro que se ajunta, pedir humildemente disculpas quiero, pues aunque grande ha sido el esfuerzo realizado nunca se llega a la perfección requerida. Quisiera para finalizar agradecer a las generaciones de estudiantes, de los cuales tanto he aprendido y sigo aprendiendo, su labor en la ejecución de este documento, su iniciativa y perspicacia son el faro que todo navegante necesita. Extensivo quiero hacer mi agradecimiento al Profesor Esteve Codina, pues diversos de los problemas que aquí se exponen salieron de su tintero. Dedico el libro a todo el colectivo universitario, del cual tanto he aprendido, aunque a veces el aprendizaje no haya sido todo lo idóneo que cabria esperar.
Article
An axial-type fan which operates at the relative total pressure of 671Pa and static pressure of 560Pa with the flow rate of 416.6m^3/min is developed with an optimization technique based on the gradient method. Prior to the optimization of fan blade, a three-dimensional axial-type fan blade is designed based on the free-vortex method along the radial direction. Twelve design variables are applied to the optimization of the rotor blade, and one design variable is selected for optimizing a stator which is located behind of the rotor and is used to support a fan driving motor. The total and static pressure are applied to the restriction condition with the operating flowrate on the design point, and the efficiency is chosen as the response variable to be maximized. Through these procedures, an initial axial-fan blade designed by the free vortex method is modified to increase the efficiency with the satisfaction of the operating condition. The optimized fan is tested to compare the aerodynamic performance with an imported same class fan. The test result shows that the optimized fan operates with the satisfaction of restriction conditions, but the imported fan cannot. From the experimental and numerical test, they show that this optimization method improves the fan efficiency and operating pressures of a fan designed by the classical fan design method.
Article
Fan performances are obtained with various tip clearance gaps and stagger angles of the rotor. A tested fan is an axial-type fan of which the casing diameter is 806 mm. Two different rotors are applied to this test. One is designed on the basis of the free vortex method along the radial direction and the other is designed using the forced vortex method. The operating conditions are varied to the ultimate off-design point as well as the deign point. Overall efficiency, total pressure and input power are compared with the tip clearance gaps and different stagger angle. The experimental results show that changing of the stagger angle has minor influence to the performance when the same rotor is applied. When the tip clearance gap is less than 5% of the rotor span, the overall efficiency, total pressure loss and input power reduction are varied linearly with the variation of the tip clearance gaps. On the design point, the overall efficiency is decreased to the rate of 2.8-2.9 to the increasing of the tip clearance, but the changing rate of the overall efficiency is alleviated when the fan operates at off-design points. In particular, this rate is more quickly declined on a fan with the rotor designed using the forced vortex method. The result of the total pressure shows that the pressure reduction rate is a 0.08-0.1 according to the tip clearance, and additionally the input power reduction rate is a 0.045-0.065 at design point.
Chapter
Wenn der Ventilator als letzte Komponente in einer Anlage angeordnet ist und direkt in die Atmosphäre oder einen großen Raum ausbläst, wird – wie in Kapitel 1 besprochen – häufig und zweckmäßig die freiausblasende Druckerhöhung.
Article
This paper describes the design of a miniature air suction system to house a chemical sensor. It has been designed to improve the aerodynamic chemical sensing efficiency and to have a low weight since it is meant to be mounted on a micro air vehicle. The design is done around a readily available miniature axial flow fan by computational methods. A converging-diverging shape for the air suction system with the sensor disc having a central hole and mounted at the throat is proposed as good design concept. The systematic approach has led to a light weight system with high aerodynamic efficiency even under extreme flow conditions that may be caused by MAV manoeuvre or cross winds.
Article
Full-text available
A low speed open circuit wind tunnel has been designed, manufactured and constructed at the Mechanical Engineering Department at Baghdad University-College of Engineering. The work is one of the pioneer projects adapted by the R & D Office at the Iraqi MOHESR. The present paper describes the first part of the work; that is the design calculations, simulation and construction. It will be followed by a second part that describes testing and calibration of the tunnel. The proposed wind tunnel has a test section with cross sectional area of (0.7 x 0.7 m 2) and length of (1.5 m). The maximum speed is about (70 m/s) with empty test section. The contraction ratio is (8.16). Three screens are used to minimize flow disturbances in the test section. The design philosophy is discussed and methods for wind tunnel calculation are outlined. Simulation of wind tunnel using ANSYS shows no separation of flow along wind tunnel. Construction steps are also included in present work.
Article
This paper presents a methodology for the aerodynamic design of reversible axial-flow rotors of jet fans, usually used for ventilation of road tunnels. Due to the low hub-to-tip ratio, typical of this kind of rotors, a particular type of non-free vortex is adopted to solve the radial equilibrium equation, in order to reduce the twist in the blades when compared to the free-vortex case. Values of the deviation and incidence angles, lift and profile drag coefficients, were interpolated from the literature data, for elliptical profiles with maximum aspect ratio of 8%. In order to reliably use these data in the computational routine, written in FORTRAN, for obtaining the main geometric and operational characteristics, a technique of scattered data interpolation was utilized. Radial basis functions (RBF) of type thin plate spline (TPS) were thus used for this purpose. This function showed to be efficient for the iterative procedure in the aerodynamic design of the rotor blades. Two reversible axial-flow rotors, formed by elliptical profiles, were finally obtained with the proposed methodology. The first profile resulted from the free-vortex condition and the second one from the non-free vortex condition. Both rotors have the same dimensions and the same number of blades, but differ in the stagger angle of each profile forming the blades. Through the use of the commercial code FLUENT, the main aerodynamic performance characteristics of these two rotors were determined, for a specific rotation, within a wide range of operation conditions. The non-free vortex rotor showed a higher maximum efficiency when compared to the free-vortex one, which was located in the region of stability of the rotor. On the contrary, the free-vortex rotor maximum efficiency was located in the region of instability of the rotor.
Conference Paper
Full-text available
A rig has been designed and constructed according to the ISO 5801 Standard, to test fans with a maximum inlet diameter equal to 0.8 m. The rig design procedure, that turned into an effective manufacturing and installation, is described. Issues that emerged from the preliminary study of the 5801 Standard are highlighted and discussed. Suggestions to improve the Standard are proposed.
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